1. Field of the Invention
This invention relates to an implantable system for stimulating electrically excitable tissue within a patient and recording potentials of such tissue in the patient, and more particularly relates to such a system in which the stimulating and recording electrodes are selectable to reduce the number of conductors to a minimum.
2. Description of the Related Art
Often it is desirable with spinal cord or deep brain stimulation for pain relief or control of movement disorders to have many stimulation electrodes on a stimulation lead in order to place one or more cathodes and one or more anodes in optimal locations to produce benefits or minimize undesirable side effects. Implanted systems now use one to three leads and have between one and sixteen stimulation electrodes. Such systems typically must pass up to 20 milliamperes of current or more, involving current densities of 10 microcoulombs per square centimeter per phase or more. As a result, each electrode is connected to a sizable conductor in order to minimize energy losses due to impedance and to provide adequate strength to connect the wire to a power supply without substantial risk of breakage. Most current systems have the ability to program the polarity of each electrode. Due to size limitations and properties of conductors, it is difficult to have high reliability when there are eight, sixteen or more wires within a lead body that is implanted in a patient.
A lead with twenty to fifty or more stimulation electrodes could be useful for some therapies. Optimal combinations of cathodes and anodes could be selected for each patient. However, the use of this many electrodes has not been feasible in the past because of the size limitations imposed by the need to have a sizable conductor connected to each electrode. The present invention is directed to solving this problem.
A tripole lead is shown in PCT Publication No. WO95/19804 (Jul. 27, 1995). However, such a lead lacks the ability to reprogram electrodes, and clinical benefit is critically dependent on electrode positioning. This invention overcomes the disadvantages of the foregoing lead by allowing changes in an effective stimulation area after implant by programming.